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The key mechanism that allows the carriers to flow without resistance in superconductors stems from an effective pairing between electrons. In conventional metallic superconductors, this pairing mechanism is well understood as phonon-mediated. In copper-oxides, the nature of the low-resistance interaction between the electrons has remained a mystery. At the same time the understanding of the puzzling properties of copper-based superconductors paves the way to finally solving the mystery of high-temperature superconductivity and revealing the key knobs for engineering new superconducting materials with even higher transition temperatures.

In an attempt to identify the microscopic interactions that drive high-temperature superconductivity in prototypical copper-oxide superconductor Bi2Sr2Ca0.92Y0.08Cu2O8+δ the international team from Italy, Japan, USA, Canada, Switzerland has used ultra-fast (100-femtosecond) laser pulses. The proposed new technique has enabled – with high resolution in both across time and across a wide range of characteristic energies – to obtain the representation of the interactions that govern the formation of the superconducting properties.

As the material's electrons relax back to an equilibrium state, they release their excess energy via deformation of the superconductor's atomic lattice (phonons) or perturbation of its magnetic correlations (spin fluctuations). The researchers were able to capture very fine grained data on the speed of the relaxation process and its influence on the properties of the superconducting system, showing that the high-critical temperature of these compounds can be accounted for by purely electronic (magnetic) processes.